/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.transforms.windowing;



import com.bff.gaia.unified.sdk.transforms.GroupByKey;

import com.bff.gaia.unified.sdk.transforms.windowing.Trigger.OnceTrigger;

import org.joda.time.Instant;



import java.util.List;



/**

 * A {@link Trigger} which never fires.

 *

 * <p>Using this trigger will only produce output when the watermark passes the end of the {@link

 * BoundedWindow window} plus the {@link Window#withAllowedLateness allowed lateness}.

 */

public final class Never {

  /**

   * Returns a trigger which never fires. Output will be produced from the using {@link GroupByKey}

   * when the {@link BoundedWindow} closes.

   */

  public static NeverTrigger ever() {

    // NeverTrigger ignores all inputs and is Window-type independent.

    return new NeverTrigger();

  }



  /** The actual trigger class for {@link Never} triggers. */

  public static class NeverTrigger extends OnceTrigger {

    private NeverTrigger() {

      super(null);

    }



    @Override

    protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {

      return this;

    }



    @Override

    public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {

      return BoundedWindow.TIMESTAMP_MAX_VALUE;

    }

  }

}